This invention relates to a movable, deformable barrier simulating the front end of an automobile for crash safety evaluation.
A movable deformable barrier (MDB), i.e., impactor, is known to be used to simulate the front end of an automobile for the purpose of crash safety evaluation. The manner of usage of the MDB is to propel the MDB into an actual automobile, typically into the side of the automobile, to impact test the side of the actual automobile for safety evaluation. The MDB must first be certified as satisfactorily simulating the front end of an actual automobile. To do this, the MDB is first mounted on a mobile sled and propelled at a predetermined specified speed for impact against a solid wall having load cells thereon. The load cells and accompanying accelerometers detect the energy absorbed by each of the segments of the MDB as it crushes, and detect the total energy absorbed by the MDB by all of its segments. If the MDB meets the predetermined specified energy absorption criteria, it is certified, then duplicates of the MDB can be used for tests. I.e., the MDB is mounted on the mobile sled and used to simulate the front end of an automobile in a crash against an actual automobile. Thus, an actual automobile to be tested is substituted for the solid wall, and the MDB crashed into the actual automobile, typically into the side thereof, to test the safety characteristics of the side doors, etc. of the automobile. To make a meaningful crash test, the MDB must have load deflection characteristics that are reasonably consistent with those of a standard size automobile. For automobiles in Europe, these characteristics have been previously determined by a European governing body and are indicated in published specifications (see FIGS. 3a-3d). The specified load deflection characteristics of the MDB have also been broken down into six segments, three in a lower row and three above them in an upper row.
During certification action, the load cell wall has specific load cell zones to measure the load generated by each corresponding section of the MDB. Thus, the load cell wall is also divided into a plurality of areas, typically six areas, with independent load cells in these areas. The energy absorption data for each load cell area must fall within the maximum and minimum boundaries of the graphical representation of the limits specified by the governing body for these areas (FIGS. 3a-3d), and the energy absorption data for the total of these load cell areas must fall within the maximum and minimum boundaries of the graph specified for the total (FIG. 3).
MDB's have been known to be made of honeycomb material. The use of honeycomb as an energy absorbing material is well known because of its uniform, consistent and predictable crush characteristics. The load deflection curve of honeycomb is actually flat after the initial deformation spike. That is to say that the resultant force generated by a section of honeycomb will remain basically constant over the entire distance of crush, as shown in FIG. 2. However, the load deflection curve specified for the MDB is not flat. Instead it ramps up at a constant rate, then levels off (FIGS. 3a-3d and 3). A known method for generating this type of force deflection curve is to shape the core to varying dimensions such that the area being crushed is proportional to the force desired by providing a pyramid shaped section of honeycomb as shown in FIG. 4. While this may generally accomplish objectives of the governmental specifications, it also generates problems. Firstly, since the load is only generated at the point of contact between the shaped honeycomb and the barrier wall, there are some areas where the local crush load may be undesirably high so as to be outside of the specifications for the individual segments (FIGS. 3a-3d). This is so even though the average over the load cell wall sections may be within the "total" force specifications limits (FIG. 3). Automobiles, however, are not homogeneous structures. There are various hard spots and soft spots in an automobile structure. Depending on where the MDB with the prior art shaped honeycomb strikes the vehicle, therefore, there can be a variety of different results. If a hard spot of the MDB were to strike a soft part of the automobile, there might be considerable penetration into the vehicle. If a hard spot on the MDB were to come into contact with a hard spot on the car, the distortion might be minimal. Secondly, the side loads generated during the impact may tend to shear the prior art core because of its small cross sectional area, resulting in unpredictable crush values.
Another prior art device is an element consisting of six single blocks of polyurethane foam with different densities. To obtain desired force to deflection characteristic, parts of the material were cut out at the rear side (barrier side) as shown in FIG. 4a.
The invention described and claimed in parent application Ser. No. 08/536,058 provides significant functional improvement over the known prior art devices. In some situations, however, the test results have shown an errant curve that briefly extends outside the specified limits. More specifically, the theoretical pattern in FIG. 9a is expected to result in the actual pattern in FIG. 9c, but might result in the pattern in FIG. 9b where a small portion of the curve is shown to extend slightly above the upper limit boundary. This has been found to potentially occur at the beginning of crush of a layer.